1. Field of the Invention
This invention relates to cosmetics which have a keratin layer softening effect and which provide a good feeling when used, to guanidine derivatives including acid addition salts thereof which have a moisturizing effect, a keratin softening effect, etc. and are useful as components of cosmetic formulations and to a process for the production thereof.
2. Discussion of the Background
The keratin layer, the outermost layer of the skin, becomes dry and rough during exposure to low temperature, low moisture, etc., conditions (e.g., in the winter season) or when contacted with detergents or solvents in excess amounts. It is thought that such changes in the skin occur when a hygroscopic water soluble component, called NMF (natural moisturizing factor), in the keratin layer is lost causing a reduction in the water content of and in the softness of the keratin layer. As a consequence, conventional cosmetics for use in softening the skin are blended with various types of moisturizing agents including natural moisturizing components such as organic acids and amino acids, for the purpose of providing the keratin layer with a large quantity of moisture for a prolonged period of time.
An example of such skin softening cosmetics are those in which an .alpha.-hydroxy acid having a keratin layer softening function is blended as an organic acid as in JP-A-55-19291 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, .alpha.-hydroxy acids have a disadvantage in that their effects are transient and can be obtained only within a low pH range (pH 2 to 4) which inhibits normal skin physiology.
In order to resolve such a problem, some cosmetics are adjusted to a neutral pH range by supplementing them with strong alkalis such as sodium hydroxide, potassium hydroxide and the like or amines such as triethanolamine and the like. These strong alkalis, however have a disadvantage in that the quality of the resulting cosmetics cannot be maintained at a constant level, because these alkalis spoil the stability of the cosmetics when blended in a large amount, and it is difficult to accommodate the pH range of the skin. Amines, on the other hand, are not desirable from a safety point of view because of the possibility to cause allergic reaction.
In order to resolve such problems caused by the blending of .alpha.-hydroxy acids, cosmetics in which .alpha.-hydroxy acids are used in combination with basic amino acids have been proposed for example in JP-B-3-30556 (the term "JP-B" as used herein means an "examined Japanese patent publication"), but their skin softening effects are not sufficient.
In addition, cosmetics blended with amino acids and their derivatives have been proposed with the aim of obtaining skin softening through improvement of the moisturizing effect, such as those in which the hydrolysate of coix seed and the like are blended (for example, JP-B-58-8007) and in which various types of peptides are blended (for example, JP-A-48-23944, JP-A-62-99315 and JP-A-2-178207). The skin softening effect of these amino acids and peptide compositions, however, are not sufficient.